Hydraulic fracturing of a stratum for mining shale gas is a method that has been practiced for a long time. Natural polysaccharides such as guar gum are often used in fracturing fluid which is used for excavating in hydraulic fracturing in order to improve the viscosity. However, when guar gum is used, it would be necessary to separately add an additional crosslinking agent in order to homogeneously gelate the entire fluid. In most cases, a boric acid-based compound with a relatively high toxicity is used as a crosslinking agent. Meanwhile, use of a water absorbent resin for fracturing fluids has been proposed in recent years.
Patent Literatures 1-4 (US Patent Application Publication No. 2014/0251610, US Patent Application Publication No. 2014/0332213, US Patent Application Publication No. 2014/0332214, and US Patent Application Publication No. 2015/0096751, respectively) disclose the use of a water absorbent resin as a fracturing fluid.
Meanwhile, Patent Literature 5 (International Publication No. WO 2008/126793) discloses a particulate water absorbent agent comprising a polyacrylate-based water-absorbent resin with a high fluid retention capacity as the main component.